In large microwave safe bowl, add butter. Microwave 45 seconds; stir, then microwave another 25 seconds. If not fully melted, whisk to melt remaining pieces.
Add sugar and whisk vigorously to incorporate. Add cocoa powder and espresso powder, if using. Whisk to blend well.
Add eggs and vanilla, and continue to whisk well. Use rubber scraper to scrape down sides and bottom of bowl so it all mixes well and fully. Mixture will start thickening and holding its shape. Set aside.
In medium bowl, add flour, baking soda, and salt and whisk to blend. With firm rubber scraper or wooden spoon, add flour mixture to chocolate mixture until just blended. Fold in both kinds of chips.
Refrigerate for about 10 minutes or while oven preheats.
Heat oven to 350 degrees. Line baking sheets with parchment paper. Use tablespoon to scoop dough and roll into balls. Place about 2 inches apart on sheet. Press down lightly on each dough ball to flatten slightly. This produces a flatter, more perfectly shaped cookie.
Bake about 10 minutes. Do not over bake. Let cool 5 minutes on baking sheet before moving to cooling rack to cool completely.